Devices to compact parts out of powder material for sintering are well known to those persons skilled in the art. In some cases, the compacted part has an undercut which prevents removal of the part or blank from the dies by linear or axial displacement.
Tool sets with split dies are known in powder material compaction to press parts into shapes that have an undercut in the compacting direction.
For example, U.S. Pat. No. 3,773,446 teaches a device for moulding parts to be sintered by compressing powdered material held between a fixed die and moveable die. A pair of punches extending through the dies compresses the powder material. A pressure plate operated by the punch extending through the moveable die engages the moveable die and is also locked to the fixed die during the compression so as to produce a part having an undercut.
U.S. Pat. No. 3,752,622 teaches a device for moulding blanks with undercut parts to be sintered by compaction of powder material.
The prior art teaches that both parts of the die are tied together while filling with a feed box that moves across the top of the dies for purpose of filling the cavity with powdered material. After compaction the upper part of the die moves away together with the top punch to eject the part.
One of the disadvantages of the known systems as referred to above relates to the fact that the upper part of the die has to be tied mechanically to the lower part of the die and the upper punch in an alternating mode, thus making a complicated tool rig necessary. This construction leads to a fixed fill height for the charge and so adjustments cannot be made to accommodate batch to batch variations. With undercut components it is necessary to ensure that powder is uniformly distributed in the die prior to compaction. The undercut areas of the component tend to inhibit flow of powder within the die and so may produce components with local zones of weakness. This non-uniformity is compounded by variations in the characteristics of the change of material so that variations in density of the powder after compression may occur.
It is therefore an object of this invention to obviate or integrate the above disadvantages to provide a device that is simpler to construct and more efficient to operate than heretofore known by the prior art.
In a first aspect of the invention there is provided a toolset for a powder molding machine comprising a pair of opposed die and punch sets each having a die and a punch co-operating therewith to define respective chambers, the sets being movable relative to one another from an open position in which the sets are separated, to a closed position in which the sets abut, with the chambers in closed communication to form a closed mold cavity, one of the punches being movable from a filling position, in which the respective chamber has a volume sufficient to receive a charge of powder to fill the cavity, to a transfer position in which the respective chamber has a reduced volume, movement of the punch between the filling and the transfer positions thereby transferring powder to the other of the chambers to fill the closed cavity.
In another aspect of the invention the pair of die and punch sets constitutes a first die and punch set and a second die and punch set; the one punch being a first punch of the first die and punch set, the die with which it co-operates being a first die of the first die and punch set, and the first die and punch set having, additionally, at least a second punch; and the first and second punches are slidably nested within the first die.
In still another aspect of the invention the dies and punches of the pair of die and punch sets are further movable to compaction and ejection positions, and, in each of the filling, transfer, compaction, and ejection positions each of the punches is in sliding engagement within the die with which it is co-operating.
In yet another aspect of the invention the die and punch sets are movable in a direction of reciprocation, and, in the closed position, one of the chambers is offset transversely to the direction relative to the other of the chambers.
In a further aspect of the invention, the dies and punches of the pair of die and punch sets are further movable to compaction and ejection positions, and, in each of the filling, transfer, compaction, and ejection positions each of the punches is in sliding engagement within the die with which it is co-operating.
In another aspect of the invention there is a press for compacting a part out of powder material, that press comprising: (a) first and second die and punch sets, the first set movable relative to the second set between open, closed, and ejection positions; (b) means for causing the first set to move relative to the second set; (c) the second die and punch set having a first die and a first punch engaged within the first punch for relative movement therebetween; (d) means for causing relative movement between the first punch and first die of the second die and punch set; (e) the first die and punch set having a first die and a first punch engaged within the first punch for relative movement therebetween; (f) means for causing relative movement between the first punch and the first die of the first die and punch set; (g) the first punch movable within the first die of the first die and punch set to define a first chamber; (h) the first punch movable within the first die of the second die and punch set to define a second chamber; (i) the means of (b) movable to place the die and punch sets in the closed position with the first and second chambers in communication to form a closed mold cavity, and to capture a charge of powder therein; (j) the means of (f) movable in the closed position to move the first punch of the first die and punch set to transfer powder from the first chamber to the second chamber; (k) at least two of the means of (b), (d) and (f) co-operable to move the punches within the dies in the closed position to compact the powder; and (l) the means of (b), (d) and (f) co-operable to move the die and punch sets to the ejection position for ejecting the part.
Another aspect of the invention is a method for making compacted powder parts with a toolset including a pair of die and punch sets each having a die and an associated punch engageable therewithin to define respective chambers, the method comprising the sequential steps of: (a) establishing the tool set in a position in which the chambers are in closed communication to form a closed mold cavity with a charge of powder captured therein; (b) moving one of the punches to transfer at least a portion of the charge of powder from one of the chambers to the other of the chambers; (c) compacting the charge of powder to form a part; and (d) ejecting the part.
In a final aspect of the invention, step (a) includes moving the die and punch sets together to a position in which the one chamber is offset from the other chamber and in closed communication therewith to form the closed mold cavity.